1. Field of the Invention
The present invention relates to an ink composition for inkjet recording and to an inkjet recording method and apparatus using the ink composition.
2. Discussion of the Background
Recently, inkjet recording methods have rapidly been in widespread use because of having the following advantages:
(1) printers used therefor are small in size and low-cost;
(2) running cost is relatively low; and
(3) printers can produce images at low noise.
Inkjet printers which can record images on a plain paper such as transfer papers for electrophotography; printing papers; recording papers for typewriter, wire-dot printers and word processors; letter papers; report papers; etc., are marketed. There are inkjet printers having a recording head having a member which contacts an ink and which is made of glass, silicone or silicone oxide because these materials can be finely processed with a high-degree of accuracy by a simple method.
As the ink for use in such inkjet printers, inks which include a solvent, and a colorant and a wetting agent (e.g., polyhydric alcohols and their ethers), which are dispersed or dissolved in the solvent are typically used. The inks optionally include a penetrant, an antimildew agent, an antiseptic agent, and a dispersant, if desired. When such inks are allowed to settle for a long period of time while set in an inkjet printer which has a recording head including members which contact the ink and which is made of glass, silicon or silicon oxide, the glass, silicon or silicon oxide is dissolved in the inks. Thereby the accuracy of dimension of the members deteriorates, resulting in changes of the size and/or discharging speed of discharged ink drops, and thereby the image qualities deteriorate or in the worst case a faulty-ink-discharge problem in which the ink to be discharged cannot be discharged or poorly discharged from nozzles occurs.
In addition, since the strength of the recording members using glass, silicon or silicon oxide deteriorates at junctions between the recording members, a faulty-ink-discharge problem occurs or in the worst case the junctions are broken, resulting in damage of the printer.
In particular, when the ink room of a recording head which contains an ink to be discharged is made of glass, silicon or silicon oxide, the dimensional accuracy of the ink room deteriorates due to dissolution of such a material into the ink and thereby the above-mentioned problems frequently occurs.
When the ink-flow-regulating portion of a recording head, which is the projected portion hear the ink room and which regulates the ink flow to the ink room, is made of glass, silicon or silicon oxide, the resistance to the ink given by the ink-flow-regulating portion changes due to dissolution of such a material into the ink, resulting in changes of size and discharge speed of the ink drops, and thereby the image qualities deteriorate and in the worst case the faulty-ink-discharging problem occurs.
When the vibrating plate of a recording head from which vibrates to discharge an ink drop from a nozzle is made of glass, silicon or silicon oxide, the thickness of the vibrating plate changes due to dissolution of the material into the ink, resulting in changes of size and discharge speed of the ink drops, and thereby the image qualities deteriorate, and in the worst case the vibrating plate is broken.
When the nozzles of a recording head from which ink drops are discharged are made of glass, silicon or silicon oxide, the size and discharge speed of the ink drops change or the faulty-ink-discharging problem occurs, and thereby the image qualities deteriorate.
In addition, when the material such as glass, silicon or silicon oxide is dissolved in an ink, the dispersibility and solubility of the colorant included in the ink are depressed, resulting in precipitation of the colorant, and thereby a nozzle-choking problem in which a nozzle is choked with an agglomerated colorant occurs. In addition, the glass, silicon or silicon itself dissolved in the ink is also precipitated at the surface of nozzles when the solvent (such as water) of the ink evaporates. Therefore the nozzle-choking problem occurs.
These problems have not yet been solved. Therefore, a method such that when an ink is ended, a new ink cartridge having an inkjet recording head and containing an ink is set in a printer has been performed without reusing the old inkjet recording head. Namely, inkjet recording heads have a short life.
In attempting to solve such problems, Japanese Laid-Open Patent Publication No. (hereinafter JOP) 05-155023 and WO98-42513 have disclosed a technique in which a layer of an inorganic material such as SiN, TiN and TiO or an organic material is formed on the members made of glass, silicon or silicon oxide. However, the manufacturing method therefor is complex, and therefore the resultant recording head and inkjet printer are very expensive. In addition, these layers typically have pinholes (i.e., film defects) and therefore it is hard to uniformly form such a layer without film defects. In addition, in some kinds of recording heads having a specific structure, such a layer cannot be formed. Further, it is recently found that even such a layer is dissolved in inks including specific black dyes. Furthermore, it is also found that such a layer is dissolved into other dyes at a concentration greater than a limit value when used for a long period of time.
JOP 09-123437 discloses a recording ink which includes urea which can stabilize the dissolved glass, silicon or silicon oxide in the ink. However, by using this technique, the dissolution of glass, silicon or silicon oxide cannot be prevented. Therefore even when this technique is used, glass, silicon or silicon oxide cannot be used for the recording members which are needed to be formed with a high-degree of accuracy, such as the ink room, ink-flow-regulating portion and vibrating plate.
Therefore a need exists for an ink which does not dissolve a substrate made of a material, such as inorganic materials such as glass, silicon, and silicon oxide which can be easily formed by heat-oxidizing silicon, and a substrate in which a layer made of an inorganic material such as SiN, TiN and TiO, or an organic material is formed on a substrate made of a material such as silicon or silicon oxide.
Japanese Patent Publication No. 07-51687 discloses an ink in which the content of sodium is specified. JOP 05-331391 discloses an ink in which the contents of sodium and potassium are specified. In addition, JOPs 08-333542 and 09-25441 have disclosed an ink in which the content of sodium is specified and an ink in which the content of potassium is specified, respectively.
Some of the present inventors and other inventors have proposed an ink in Japanese Patent No. 1,677,642 (i.e., JOP 62-149770), which includes a dye and a specific compound having a quaternary ammonium ion as a counter ion, and an ink in Japanese Patent No., 2,085,163 (i.e., JOP 63-048374), which includes a specific dye having a quaternary phosphonium ion as a counter ion. These proposals have been made for solving the nozzle-choking problem and kogation, and the inks have good preservation property. However, such a dissolution problem did not become obvious at that time when the applications for these patents were filed and whether or not the material such as glass, silicon and silicon oxide is dissolved by these inks has not been examined. When the present inventors evaluate these inks recently, it is found that the above-mentioned dissolution problem of the material such as glass, silicon and silicon oxide cannot be fully solved.
In addition, pigments have been used as colorants for recording inks, but pigments have a drawback such that the resultant recording inks have relatively poor discharge stability compared to that of dye inks. In attempting to solve this problem, proposals in which pigments whose surface is modified and microencapsulated pigments are used without using a dispersant which tends to cause a nozzle-choking problem have been made in JOPs 10-183003, 11-343439, 11-349870 and 2000-007961. However, in these background art, the dissolution problem in which glass, silicon and/or silicon oxide is dissolved in an ink and which is described in this application is never described, and the objects of the background art are to improve the dispersion stability, and abrasion resistance and water resistance of recorded images.
Because of these reasons, a need exists for a recording ink which can stably record high quality images for a long period of time without causing the dissolution problem, the faulty-ink-discharging problem, and the nozzle-choking problem.
Accordingly, an object of the present invention is to provide an ink composition for inkjet recording which can stably record an ink image by discharging ink drops having a uniform size and which does not cause the faulty-ink-discharging problem, the nozzle-choking problem and the dissolution problem even when the ink contacts an recording member, such as the ink room, ink-flow-regulating portion, and vibrating plate, made of a material such as glass (e.g., boron silicate glass, photosensitive glass, quartz glass, soda lime glass) and silicon (e.g., single crystal silicon and polysilicon), or a material in which a layer of an oxide such as silicon oxide, titanium oxide, and chromium oxide, a nitride such as titanium nitride and silicon nitride, a metal such as zirconium, or an organic material such as polyimides is formed on a support of silicon or glass.
Another object of the present invention is to provide an inkjet recording method and apparatus by which high quality images can be produced without causing the faulty-ink-discharging problem, nozzle-choking problem and dissolution problem even when the above-mentioned material is used for the recording member which contacts the ink used.
Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by an ink composition including a colorant and a solvent, wherein the zeta potential (hereinafter zeta potential 2) between the colorant and a material selected from the group consisting of silicon, glass, silicon oxide, titanium oxide, chromium oxide, titanium nitride, silicon nitride, zirconium and polyimide is from 0 to xe2x88x9250 mV at a pH of from 6.5 to 11.5.
The zeta potential of the ink itself (hereinafter referred to as zeta potential 1) at a pH of from 6.5 to 11.5 is preferably not greater than xe2x88x9220 mV.
The colorant is preferably covered with a resin or a particulate resin colored with a coloring agent is preferably used as the colorant.
The colorant may be microencapsulated. The shell of the microcapsule is preferably made of a hydrophilic resin. Preferably a microencapsulated pigment is used as the colorant. The average particle diameter of the microcapsule is preferably from 0.01 to 0.2 xcexcm, and the pigment is included in the ink in an amount of from 0.1 to 10% by weight.
The ink composition preferably includes a corrosion inhibitor such as a cation or a cationic compound to adjust the zeta potentials 1 and 2. The cationic compound is preferably a cationic resin, a cationic surfactant or a cationic colorant such as cationic dyes, cationic carbon black and cationic pigments.
The cation is preferably a cation selected from the group consisting of a phosphonium ion having the following formula (1): 
wherein Ra, Rb, Rc and Rd independently represent a linear, branched or ring alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group, a halogenated alkyl group, or a substituted or unsubstituted phenyl group;
a sulfonium ion having the following formula (3): 
wherein Ra, Rb and Rc independently represent a linear, branched or ring alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group, a halogenated alkyl group, or a substituted or unsubstituted phenyl group;
an arsonium ion having the following formula (4): 
wherein Ra, Rb, Rc and Rd independently represent a linear, branched or ring alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group, a halogenated alkyl group, or a substituted or unsubstituted phenyl group;
a beryllium ion (Be2+); an aluminum ion (Al3+); a zinc ion (Zn2+), a titanium ion (Ti4+); a zirconium ion (Zr4+); and a silicide ion (Si2+).
Semi-polar boron compounds can also be included in the ink composition.
The ink preferably includes an acetylene compound having the following formula (2): 
wherein R1 to R6 independently represent a linear alkyl group having from 1 to 5 carbon atoms; and m and n is 0 or an integer of from 1 to 20.
These cations and cationic compounds may be included alone or in combination.
The pH of the ink composition is preferably from 7 to 10.
The ink component of the present invention is preferably used for an inkjet printer having a recording head which includes at least an ink room, an ink-flow-regulating portion, a vibrating plate and an inkjet nozzle, wherein at least one part of each of these members is made of silicon (preferably single crystal silicon or polysilicon), glass (preferably boron silicate glass, photosensitive glass, quartz glass or soda lime glass) or a material in which a layer of an oxide (preferably silicon oxide, titanium oxide or chromium oxide), a nitride (preferably titanium nitride or silicon nitride), a metal (preferably zirconium) or an organic compound (preferably polyimide) is formed on a substrate of silicon or glass.
In another aspect of the present invention, an inkjet recording method is disclosed which includes the steps of discharging an ink from a nozzle of a recording head having at least an ink room, an ink-flow-regulating portion, a vibrating plate and the nozzle to form an ink image of a recording paper, wherein the ink is the ink of the present invention and at least one part of each of the ink room, ink-flow-regulating portion, vibrating plate and nozzle, which contacts the ink, is made of silicon (preferably single crystal silicon or polysilicon), glass (preferably boron silicate glass, photosensitive glass, quartz glass, or soda lime glass) or a material in which a layer of an oxide (preferably silicon oxide, titanium oxide or chromium oxide), a nitride (preferably titanium nitride or silicon nitride), a metal (preferably zirconium) or an organic compound (preferably polyimide is formed on a substrate of silicon or glass).
In the inkjet recording method, the ink room, ink-flow-regulating portion, vibration plate and nozzle are preferably prepared by a method selected from the group consisting of etching treatments, sand blast treatments, excimer laser treatments and drilling treatments.
In yet another aspect of the present invention, an ink cartridge is provided which includes an ink container containing the ink of the present invention.
The ink cartridge preferably may have a recording head including an ink room, an ink-flow-regulating portion, a vibrating plate and a nozzle from which the ink is discharged.
In a further aspect of the present invention, an inkjet recording apparatus is provided which includes the ink cartridge of the present invention, which includes the ink of the present invention and a carriage configured to carry the ink cartridge to form an ink image on a recording paper.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.